Ok, thanks for the answer, it works now, even with 3g and several LAN. I will post my conf files in the thread you mentionned for helping someone 
EDIT : Done at https://help.nextcloud.com/t/complete-nc-installation-on-debian-with-spreed-me-and-turn-step-by-step/2436/38
Spreed app canāt connect to my TURN server, I tried : https://mynextcloud.net:8443, ip:8443, mynextcloud.net:8443, and several ways, but it doesnāt workā¦